The PageRequestManager cannot be initialized more than once - UpdatePanel - Sharepoint 2013

I am new to Sharepoint 2013, I have created a WebPart using Visual Studio 2013 and Deployed into my site, I have googled lots about this issue but not found any solution.

I am using UpdatePanel and Page postback when I click on button and when i debug the code using IE I got the following issue:

ScriptResource.axd:
throw Error.invalidOperation(Sys.WebForms.Res.PRM_CannotRegisterTwice) The PageRequestManager cannot be initialized more than once

VisualWebPart.ascx:

<asp:ScriptManager runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>

        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
        <asp:LinkButton ID="Button1" runat="server" Text="Button" OnClick="Button1_Click1" />

    </ContentTemplate>

</asp:UpdatePanel>

VisualWebPart.ascx.cs:

public partial class VisualWebPart1 : WebPart
    {
        public VisualWebPart1()
        {
        }

        protected override void OnInit(EventArgs e)
        {            
            base.OnInit(e);
            InitializeControl();
        }

        protected void Page_Load(object sender, EventArgs e)
        {
        }

        protected void Button1_Click1(object sender, EventArgs e)
        {
            Label1.Text = "My name is Afaaf";
        }
    }